MLS will never make it in the US. It isn’t in our nature to like it. If football falls UFC will rise to take it’s place.
MLS will make it, by directing its efforts to a smaller fan base. A stadium built in a neighboring town for the NY Red Bulls is MUCH smaller than Giants Stadium in the Meadowlands (where they played before); it is a sustainable model (though the womens’ leagues have little chance due to lack of interest).
The MLS is like European Professional Basketball, it will never match the NBA.